Many biological samples (e.g., in clinical, diagnostic, and research settings) include matrix compounds such as proteins, peptides, and phospholipids. Such samples include, for example, plasma, sera, secretions, body fluids, cells, and tissues. However, in a broader sense, a sample can include any mixture which an individual desires to separate or analyze. A mixture can be a fluid (e.g., including water and/or other liquids and gases) including one or more dissolved or suspended compounds (e.g., a compound of interest or an analyte). To study and/or analyze such samples, at least one matrix compound can be separated, removed, concentrated, and/or isolated. Such methods of separating, removing, concentrating, and/or isolating one or more compounds found in a mixture or sample are generally known as chromatography.
Chromatography can separate, remove, concentrate, and/or isolate a compound based upon a difference between the compound's affinity for the sample and the compound's affinity for a second phase (e.g., chromatography media). Chromatography can be facilitated by the relative movement of the sample and the second phase. For example, the mixture (e.g., a mobile phase) is generally moved in relation to a packed bed of particles or a porous monolith structure (e.g., a stationary phase).
Samples from biological sources such as blood, plasma, tissues, secretions, and the like often include combinations of various proteins, peptides, and/or phospholipids. Such samples can also include smaller molecules and/or other compounds of interest. Proteins and peptides are polymers of amino acids and are often present in samples. Phospholipids are class of lipids that contain a phosphate functional group and a more hydrophobic functional group. Another class of lipids, glycerophospholipids, contains one or two long saturated and/or unsaturated hydrocarbon tails attached to a glycerol residue which contains at the C-1 position a derivatized phosphoric acid polar head group. The composition of the polar head group is a phosphoric acid group derivatized by choline, serine, or ethanolamine to form phosphatidylcholine, phosphatidylserine, or phosphatidylethanolamine lipids, respectively. Smaller molecules (e.g., small organic molecule such as drugs or drug candidates) can have a wide range of chemical and physical properties. The broad differences in chemical and physical properties between mixtures of such components can present a chromatographic challenge.